The present invention relates generally to antenna assemblies and, more particularly, to an antenna assembly, and an associated method, for a portable radio operable to transmit or receive, or both transmit and receive, high-frequency, modulated signals.
A communication system is comprised, at a minimum, of a transmitter and a receiver interconnected by a transmission channel. A communication signal is transmitted upon the transmission channel, thereafter to be received by the receiver.
A radio communication system is a communication system in which the transmission channel comprises a radio frequency channel wherein the radio frequency channel is defined by a range of frequencies of the electromagnetic frequency spectrum. A transmitter operative in a radio communication system converts the communication signal to be transmitted into a form suitable for transmission thereof upon the radio frequency channel.
Conversion of the communication signal into the form suitable for the transmission thereof upon the radio frequency channel is effectuated by a process referred to as modulation. In such a process, the communication signal is impressed upon an electromagnetic wave. The electromagnetic wave is commonly referred to as a "carrier signal." The resultant signal, once modulated by the communication signal, is referred to as a modulated carrier signal, or, more simply, a modulated signal. The transmitter includes circuitry operative to perform such a modulation process.
Because the modulated signal may be transmitted through free space over large distances, radio communication systems are widely utilized to effectuate communication between a transmitter and a remotely-positioned receiver.
The receiver of the radio communication system which receives the modulated carrier signal contains circuitry analogous to, but operative in a manner reverse with that of, the circuitry of the transmitter and is operative to perform a process referred to as demodulation.
Numerous modulated carrier signals may be simultaneously transmitted as long as the signals are transmitted along differing radio frequency channels defined upon the electromagnetic frequency spectrum. Regulatory bodies have divided portions of the electromagnetic frequency spectrum into frequency bands and have regulated transmission of the modulated signals upon various ones of the frequency bands. The frequency bands are further divided into channels, and such channels form the radio frequency channels of a radio communication system. It is of course to be understood that separate channels may be defined over a single range of frequencies when signals are transmitted in a discontinuous manner, such as, e.g., in a time division multiple access (TDMA) communication scheme.
A two-way radio communication system is a radio communication system, similar to the radio communication system above-described, but which permits both transmission of a modulated signal from a location and reception at such location of a modulated signal. Each location of such a two-way communication system contains both a transmitter and a receiver. The transmitter and the receiver positioned together at the single location typically comprise a unit referred to as a radio transceiver or, more simply, a transceiver.
A cellular communication system is one type of two-way radio communication system and, when operative, communication is permitted with a radio transceiver positioned at any location within a geographic area encompassed by the cellular communication system.
A cellular communication system is created by positioning a plurality of fixed-site radio transceivers, referred to as base stations, at spaced-apart locations throughout a geographic area. The base stations are connected to a conventional, wireline, telephonic network. Associated with each base station of the plurality of base stations is a portion of the geographic area encompassed by the cellular communication system. Such portions are referred to as cells. Each of the plurality of cells is defined by one of the base stations of the plurality of base stations, and the plurality of cells together define the coverage area of the cellular communication system.
A radio transceiver, referred to in a cellular communication system as a cellular radiotelephone or, more simply, a cellular phone, positioned at any location within the coverage area of the cellular communication system, is able to communicate with a user of the conventional, wireline, telephonic network by way of a base station. Modulated signals generated by the radiotelephone are transmitted to a base station, and modulated signals generated by the base station are transmitted to the radiotelephone, thereby to effectuate two-way communication therebetween. (A signal received by a base station is then transmitted to a desired location of a conventional, wireline network by conventional telephony techniques. And, signals generated at a location of the wireline network are transmitted to a base station by conventional telephony techniques, thereafter to be transmitted to the radiotelephone by the base station.)
Certain designs of radio transceivers operable in cellular communication systems, as well as other radio communication systems, are of dimensions permitting their carriage by a user. Such portable radio transceivers are typically comprised of telephonic handsets which are somewhat analogous in appearance with telephonic handsets of conventional, telephonic apparatus. Namely, such portable transceivers include speaker portions and microphone portions supported in the handsets at spaced distances permitting a user thereof simultaneously to listen to signals transmitted to the transceiver and to generate signals therefrom.
The transceiver circuitry of a portable transceiver is housed within a transceiver housing body defining the dimensions of the handset and, typically, a single antenna is coupled to such transceiver circuitry. The antenna typically extends at a height (i.e., elevation) beyond the transceiver housing body to permit emanation of modulated signals generated during operation of the radio transceiver and to permit reception of modulated signals transmitted thereto.
The antenna utilized for such a portable radio transceiver is usually designed to form a nondirectional antenna as the user of the portable radio transceiver may position the transceiver in almost any orientation relative to a remote site (in a cellular communication system, such remote site comprises a base station) to which, or from which, modulated signals are transmitted during operation of the transceiver. That is to say, the user of the portable radio transceiver may operate the transceiver when the transceiver is positioned in either a direction directed away or a direction directed towards, or in any direction therebetween, relative to the remote site.
For best reception, such antennas are further usually of lengths substantially corresponding to fractional wavelengths of signals to be received by, or transmitted from, the antenna. More particularly, the lengths of such antennas are typically of either one-half or one-quarter wavelengths of such signals.
With respect to cellular communication systems, existing systems are operable in a frequency band having frequencies in the upper-hundreds of Megahertz. For instance, in the United States, a frequency band comprised of selected radio frequency channels between 800 Megahertz and 900 Megahertz are assigned for use by cellular communications systems. The magnitudes of one-half and one-quarter wavelengths of signals transmitted at such frequencies are of lengths of approximately seventeen and nine centimeters, respectively (or approximately seven and three inches, respectively).
A one-half wavelength antenna of such a length extending beyond a portable radio transceiver housing body also extends a distance beyond the body of a user when the user positions the transceiver for operation thereof. Hence, shadowing caused by the body of a user does not significantly interfere with transmission or reception of signals by such an antenna which extends beyond the transceiver housing body by a distance approaching--configuring the antenna in the form of the helix somewhat reduces the height at which the antenna so-formed extends beyond the housing body--seventeen centimeters (or seven inches). (The term shadowing is used to describe absorption of modulated signals by an object, usually positioned proximate to an antenna, which prevents desired reception by the antenna or transmission to a remote site, of a modulated signal. When an antenna, here an antenna affixed to a radio transceiver, is positioned proximate to an individual, the individual causes shadowing, the effect of which interferes with signal propagation to and from the antenna.)
Newly-proposed radio communication systems are to be operable at much higher frequencies--namely, in the 1.8 Gigahertz (GHz) range. Such a frequency range is more than twice as great as the just-mentioned 800-900 Megahertz range at which existing, cellular communication systems in the United States are operable.
At such increased frequencies, the lengths of one-half and one-quarter wavelength antennas forming portions of radio transceivers operable at such increased frequencies are of lengths less than one-half of the lengths of corresponding antennas of lengths of one-half and one-quarter wavelengths operable in radio transceivers of the existing, cellular communication systems. (For instance, an antenna of a length of a one-half wavelength of a 1.8 Gigahertz signal is of a length of approximately eight and one third centimeters or three and one quarter inches.) Antennas of such lengths extending beyond radio transceiver bodies do not extend for distances great enough to avoid significant shadowing effects by the body of a user when operating a radio transceiver to transmit or to receive modulated signals of such frequencies.
What is needed, therefore, is an antenna assembly for a radio transceiver operable to transmit or to receive signals at such increased frequencies which may be positioned to extend beyond the radio transceiver a distance great enough so that shadowing does not significantly affect operation of the radio.